US Sinking of Iranian Warship IRIS Dena Sparks International Law Debate

Source: The Indian Express 

Introduction 

A US submarine recently torpedoed Iranian frigate IRIS Dena approximately 40 nautical miles off the southern coast of Sri Lanka, killing over 80 sailors and injuring 32 more. The warship was returning from India's International Fleet Review — a multilateral naval exercise hosted at Visakhapatnam — when it was struck without warning in international waters. US Defence Secretary Pete Hegseth confirmed the attack.  

• The incident raises three central questions of international law:  
  • Was IRIS Dena a legitimate military target?  
  • Did the laws of armed conflict apply?  
  • And did the US Navy fulfil its duty to rescue survivors?

What is Frigate IRIS Dena? 

• IRIS Dena is a domestically built Iranian warship equipped with anti-ship "Qader" missiles, marking only the second warship torpedoed by a submarine since World War II.  
• Crucially, participation in the multilateral fleet review required its weapon systems to be kept non-operational — what geostrategist Dr. Brahma Chellaney describes as standard "peace protocols."  
• Iranian Foreign Minister Araghchi confirmed it was struck without warning, carrying mostly non-combatants and ceremonial staff.

Which Law Applies? 

Two frameworks are relevant.  

• Under US domestic law, formal war requires congressional authorisation under the War Powers Resolution, 1973, though presidents routinely bypass this via "anticipatory self-defence" under Article II of the Constitution. Under international law, while Article 2(4) of the UN Charter prohibits force, Article 51 permits self-defence — but only where necessity is "instant, overwhelming, and leaving no choice of means," per the 1837 Caroline test. 
• In peacetime, UNCLOS would govern, affording warships sovereign immunity in international waters. Since an armed conflict is underway, however, International Humanitarian Law (IHL) takes precedence as lex specialis, regulating force through the principles of distinction, proportionality, and necessity. 

Was IRIS Dena a Legitimate Target? 

• Under Article 52 of Additional Protocol I, a military objective must satisfy two conditions: it must effectively contribute to military action, and its destruction must yield a definite military advantage.  
• Warships qualify by nature — but IRIS Dena's weapons were non-operational, it showed no active hostility, and it was over 2,000 km from any recognised combat zone. Applying the Caroline test, no imminent threat is apparent.  
• What concrete military advantage was achieved by attacking the vessel this far from the conflict theatre remains entirely unestablished.

Was There a Duty to Rescue? 

• Once attacked, surviving sailors became hors de combat — persons rendered defenceless through shipwreck.  
• Rule 47 of the ICRC Customary IHL Study and Article 41(1) of Additional Protocol I prohibit targeting such persons, while Article 18 of Geneva Convention II mandates that parties take "all possible measures," without delay, to search for and collect the shipwrecked. 
• This obligation carries no reservations. While submarines may face operational constraints in surfacing, this does not extinguish the duty — they must still assess alternatives, such as alerting nearby coastal authorities. Historical precedent from WWII shows German U-boats discharging this obligation after sinking Allied vessels. Wilful failure to act constitutes a grave breach of IHL and may amount to a war crime attracting individual criminal responsibility.

Conclusion 

The sinking of IRIS Dena — unarmed, far from any combat zone, returning from a friendly naval exercise — raises serious questions under both the Caroline doctrine and IHL's principle of military necessity. More immediately, the apparent failure to rescue over 100 sailors adrift near Sri Lanka may constitute a clear violation of Article 18 of Geneva Convention II. As the undeclared conflict between the US, Israel, and Iran escalates, this incident will likely become a significant test case for the enforcement of international humanitarian law in modern naval warfare.